net/ipv4/netfilter/nf_nat_snmp_basic.c

   1 /*
   2  * nf_nat_snmp_basic.c
   3  *
   4  * Basic SNMP Application Layer Gateway
   5  *
   6  * This IP NAT module is intended for use with SNMP network
   7  * discovery and monitoring applications where target networks use
   8  * conflicting private address realms.
   9  *
  10  * Static NAT is used to remap the networks from the view of the network
  11  * management system at the IP layer, and this module remaps some application
  12  * layer addresses to match.
  13  *
  14  * The simplest form of ALG is performed, where only tagged IP addresses
  15  * are modified.  The module does not need to be MIB aware and only scans
  16  * messages at the ASN.1/BER level.
  17  *
  18  * Currently, only SNMPv1 and SNMPv2 are supported.
  19  *
  20  * More information on ALG and associated issues can be found in
  21  * RFC 2962
  22  *
  23  * The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory
  24  * McLean & Jochen Friedrich, stripped down for use in the kernel.
  25  *
  26  * Copyright (c) 2000 RP Internet (www.rpi.net.au).
  27  *
  28  * This program is free software; you can redistribute it and/or modify
  29  * it under the terms of the GNU General Public License as published by
  30  * the Free Software Foundation; either version 2 of the License, or
  31  * (at your option) any later version.
  32  * This program is distributed in the hope that it will be useful,
  33  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  34  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  35  * GNU General Public License for more details.
  36  * You should have received a copy of the GNU General Public License
  37  * along with this program; if not, write to the Free Software
  38  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  39  *
  40  * Author: James Morris <jmorris@intercode.com.au>
  41  */
  42 #include <linux/module.h>
  43 #include <linux/moduleparam.h>
  44 #include <linux/types.h>
  45 #include <linux/kernel.h>
  46 #include <linux/slab.h>
  47 #include <linux/in.h>
  48 #include <linux/ip.h>
  49 #include <linux/udp.h>
  50 #include <net/checksum.h>
  51 #include <net/udp.h>
  52
  53 #include <net/netfilter/nf_nat.h>
  54 #include <net/netfilter/nf_conntrack_expect.h>
  55 #include <net/netfilter/nf_conntrack_helper.h>
  56 #include <net/netfilter/nf_nat_helper.h>
  57 #include <linux/netfilter/nf_conntrack_snmp.h>
  58
  59 MODULE_LICENSE("GPL");
  60 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  61 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  62 MODULE_ALIAS("ip_nat_snmp_basic");
  63
  64 #define SNMP_PORT 161
  65 #define SNMP_TRAP_PORT 162
  66 #define NOCT1(n) (*(u8 *)(n))
  67
  68 static int debug;
  69 static DEFINE_SPINLOCK(snmp_lock);
  70
  71 /*
  72  * Application layer address mapping mimics the NAT mapping, but
  73  * only for the first octet in this case (a more flexible system
  74  * can be implemented if needed).
  75  */
  76 struct oct1_map
  77 {
  78         u_int8_t from;
  79         u_int8_t to;
  80 };
  81
  82
  83 /*****************************************************************************
  84  *
  85  * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
  86  *
  87  *****************************************************************************/
  88
  89 /* Class */
  90 #define ASN1_UNI        0       /* Universal */
  91 #define ASN1_APL        1       /* Application */
  92 #define ASN1_CTX        2       /* Context */
  93 #define ASN1_PRV        3       /* Private */
  94
  95 /* Tag */
  96 #define ASN1_EOC        0       /* End Of Contents */
  97 #define ASN1_BOL        1       /* Boolean */
  98 #define ASN1_INT        2       /* Integer */
  99 #define ASN1_BTS        3       /* Bit String */
 100 #define ASN1_OTS        4       /* Octet String */
 101 #define ASN1_NUL        5       /* Null */
 102 #define ASN1_OJI        6       /* Object Identifier  */
 103 #define ASN1_OJD        7       /* Object Description */
 104 #define ASN1_EXT        8       /* External */
 105 #define ASN1_SEQ        16      /* Sequence */
 106 #define ASN1_SET        17      /* Set */
 107 #define ASN1_NUMSTR     18      /* Numerical String */
 108 #define ASN1_PRNSTR     19      /* Printable String */
 109 #define ASN1_TEXSTR     20      /* Teletext String */
 110 #define ASN1_VIDSTR     21      /* Video String */
 111 #define ASN1_IA5STR     22      /* IA5 String */
 112 #define ASN1_UNITIM     23      /* Universal Time */
 113 #define ASN1_GENTIM     24      /* General Time */
 114 #define ASN1_GRASTR     25      /* Graphical String */
 115 #define ASN1_VISSTR     26      /* Visible String */
 116 #define ASN1_GENSTR     27      /* General String */
 117
 118 /* Primitive / Constructed methods*/
 119 #define ASN1_PRI        0       /* Primitive */
 120 #define ASN1_CON        1       /* Constructed */
 121
 122 /*
 123  * Error codes.
 124  */
 125 #define ASN1_ERR_NOERROR                0
 126 #define ASN1_ERR_DEC_EMPTY              2
 127 #define ASN1_ERR_DEC_EOC_MISMATCH       3
 128 #define ASN1_ERR_DEC_LENGTH_MISMATCH    4
 129 #define ASN1_ERR_DEC_BADVALUE           5
 130
 131 /*
 132  * ASN.1 context.
 133  */
 134 struct asn1_ctx
 135 {
 136         int error;                      /* Error condition */
 137         unsigned char *pointer;         /* Octet just to be decoded */
 138         unsigned char *begin;           /* First octet */
 139         unsigned char *end;             /* Octet after last octet */
 140 };
 141
 142 /*
 143  * Octet string (not null terminated)
 144  */
 145 struct asn1_octstr
 146 {
 147         unsigned char *data;
 148         unsigned int len;
 149 };
 150
 151 static void asn1_open(struct asn1_ctx *ctx,
 152                       unsigned char *buf,
 153                       unsigned int len)
 154 {
 155         ctx->begin = buf;
 156         ctx->end = buf + len;
 157         ctx->pointer = buf;
 158         ctx->error = ASN1_ERR_NOERROR;
 159 }
 160
 161 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
 162 {
 163         if (ctx->pointer >= ctx->end) {
 164                 ctx->error = ASN1_ERR_DEC_EMPTY;
 165                 return 0;
 166         }
 167         *ch = *(ctx->pointer)++;
 168         return 1;
 169 }
 170
 171 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
 172 {
 173         unsigned char ch;
 174
 175         *tag = 0;
 176
 177         do
 178         {
 179                 if (!asn1_octet_decode(ctx, &ch))
 180                         return 0;
 181                 *tag <<= 7;
 182                 *tag |= ch & 0x7F;
 183         } while ((ch & 0x80) == 0x80);
 184         return 1;
 185 }
 186
 187 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
 188                                     unsigned int *cls,
 189                                     unsigned int *con,
 190                                     unsigned int *tag)
 191 {
 192         unsigned char ch;
 193
 194         if (!asn1_octet_decode(ctx, &ch))
 195                 return 0;
 196
 197         *cls = (ch & 0xC0) >> 6;
 198         *con = (ch & 0x20) >> 5;
 199         *tag = (ch & 0x1F);
 200
 201         if (*tag == 0x1F) {
 202                 if (!asn1_tag_decode(ctx, tag))
 203                         return 0;
 204         }
 205         return 1;
 206 }
 207
 208 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
 209                                         unsigned int *def,
 210                                         unsigned int *len)
 211 {
 212         unsigned char ch, cnt;
 213
 214         if (!asn1_octet_decode(ctx, &ch))
 215                 return 0;
 216
 217         if (ch == 0x80)
 218                 *def = 0;
 219         else {
 220                 *def = 1;
 221
 222                 if (ch < 0x80)
 223                         *len = ch;
 224                 else {
 225                         cnt = ch & 0x7F;
 226                         *len = 0;
 227
 228                         while (cnt > 0) {
 229                                 if (!asn1_octet_decode(ctx, &ch))
 230                                         return 0;
 231                                 *len <<= 8;
 232                                 *len |= ch;
 233                                 cnt--;
 234                         }
 235                 }
 236         }
 237
 238         /* don't trust len bigger than ctx buffer */
 239         if (*len > ctx->end - ctx->pointer)
 240                 return 0;
 241
 242         return 1;
 243 }
 244
 245 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 246                                         unsigned char **eoc,
 247                                         unsigned int *cls,
 248                                         unsigned int *con,
 249                                         unsigned int *tag)
 250 {
 251         unsigned int def, len;
 252
 253         if (!asn1_id_decode(ctx, cls, con, tag))
 254                 return 0;
 255
 256         def = len = 0;
 257         if (!asn1_length_decode(ctx, &def, &len))
 258                 return 0;
 259
 260         /* primitive shall be definite, indefinite shall be constructed */
 261         if (*con == ASN1_PRI && !def)
 262                 return 0;
 263
 264         if (def)
 265                 *eoc = ctx->pointer + len;
 266         else
 267                 *eoc = NULL;
 268         return 1;
 269 }
 270
 271 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 272 {
 273         unsigned char ch;
 274
 275         if (eoc == NULL) {
 276                 if (!asn1_octet_decode(ctx, &ch))
 277                         return 0;
 278
 279                 if (ch != 0x00) {
 280                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 281                         return 0;
 282                 }
 283
 284                 if (!asn1_octet_decode(ctx, &ch))
 285                         return 0;
 286
 287                 if (ch != 0x00) {
 288                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 289                         return 0;
 290                 }
 291                 return 1;
 292         } else {
 293                 if (ctx->pointer != eoc) {
 294                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 295                         return 0;
 296                 }
 297                 return 1;
 298         }
 299 }
 300
 301 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 302 {
 303         ctx->pointer = eoc;
 304         return 1;
 305 }
 306
 307 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 308                                       unsigned char *eoc,
 309                                       long *integer)
 310 {
 311         unsigned char ch;
 312         unsigned int  len;
 313
 314         if (!asn1_octet_decode(ctx, &ch))
 315                 return 0;
 316
 317         *integer = (signed char) ch;
 318         len = 1;
 319
 320         while (ctx->pointer < eoc) {
 321                 if (++len > sizeof (long)) {
 322                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 323                         return 0;
 324                 }
 325
 326                 if (!asn1_octet_decode(ctx, &ch))
 327                         return 0;
 328
 329                 *integer <<= 8;
 330                 *integer |= ch;
 331         }
 332         return 1;
 333 }
 334
 335 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 336                                       unsigned char *eoc,
 337                                       unsigned int *integer)
 338 {
 339         unsigned char ch;
 340         unsigned int  len;
 341
 342         if (!asn1_octet_decode(ctx, &ch))
 343                 return 0;
 344
 345         *integer = ch;
 346         if (ch == 0) len = 0;
 347         else len = 1;
 348
 349         while (ctx->pointer < eoc) {
 350                 if (++len > sizeof (unsigned int)) {
 351                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 352                         return 0;
 353                 }
 354
 355                 if (!asn1_octet_decode(ctx, &ch))
 356                         return 0;
 357
 358                 *integer <<= 8;
 359                 *integer |= ch;
 360         }
 361         return 1;
 362 }
 363
 364 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 365                                        unsigned char *eoc,
 366                                        unsigned long *integer)
 367 {
 368         unsigned char ch;
 369         unsigned int  len;
 370
 371         if (!asn1_octet_decode(ctx, &ch))
 372                 return 0;
 373
 374         *integer = ch;
 375         if (ch == 0) len = 0;
 376         else len = 1;
 377
 378         while (ctx->pointer < eoc) {
 379                 if (++len > sizeof (unsigned long)) {
 380                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 381                         return 0;
 382                 }
 383
 384                 if (!asn1_octet_decode(ctx, &ch))
 385                         return 0;
 386
 387                 *integer <<= 8;
 388                 *integer |= ch;
 389         }
 390         return 1;
 391 }
 392
 393 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 394                                         unsigned char *eoc,
 395                                         unsigned char **octets,
 396                                         unsigned int *len)
 397 {
 398         unsigned char *ptr;
 399
 400         *len = 0;
 401
 402         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 403         if (*octets == NULL)
 404                 return 0;
 405
 406         ptr = *octets;
 407         while (ctx->pointer < eoc) {
 408                 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
 409                         kfree(*octets);
 410                         *octets = NULL;
 411                         return 0;
 412                 }
 413                 (*len)++;
 414         }
 415         return 1;
 416 }
 417
 418 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 419                                        unsigned long *subid)
 420 {
 421         unsigned char ch;
 422
 423         *subid = 0;
 424
 425         do {
 426                 if (!asn1_octet_decode(ctx, &ch))
 427                         return 0;
 428
 429                 *subid <<= 7;
 430                 *subid |= ch & 0x7F;
 431         } while ((ch & 0x80) == 0x80);
 432         return 1;
 433 }
 434
 435 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 436                                      unsigned char *eoc,
 437                                      unsigned long **oid,
 438                                      unsigned int *len)
 439 {
 440         unsigned long subid;
 441         unsigned long *optr;
 442         size_t size;
 443
 444         size = eoc - ctx->pointer + 1;
 445
 446         /* first subid actually encodes first two subids */
 447         if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
 448                 return 0;
 449
 450         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 451         if (*oid == NULL)
 452                 return 0;
 453
 454         optr = *oid;
 455
 456         if (!asn1_subid_decode(ctx, &subid)) {
 457                 kfree(*oid);
 458                 *oid = NULL;
 459                 return 0;
 460         }
 461
 462         if (subid < 40) {
 463                 optr [0] = 0;
 464                 optr [1] = subid;
 465         } else if (subid < 80) {
 466                 optr [0] = 1;
 467                 optr [1] = subid - 40;
 468         } else {
 469                 optr [0] = 2;
 470                 optr [1] = subid - 80;
 471         }
 472
 473         *len = 2;
 474         optr += 2;
 475
 476         while (ctx->pointer < eoc) {
 477                 if (++(*len) > size) {
 478                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 479                         kfree(*oid);
 480                         *oid = NULL;
 481                         return 0;
 482                 }
 483
 484                 if (!asn1_subid_decode(ctx, optr++)) {
 485                         kfree(*oid);
 486                         *oid = NULL;
 487                         return 0;
 488                 }
 489         }
 490         return 1;
 491 }
 492
 493 /*****************************************************************************
 494  *
 495  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 496  *
 497  *****************************************************************************/
 498
 499 /* SNMP Versions */
 500 #define SNMP_V1                         0
 501 #define SNMP_V2C                        1
 502 #define SNMP_V2                         2
 503 #define SNMP_V3                         3
 504
 505 /* Default Sizes */
 506 #define SNMP_SIZE_COMM                  256
 507 #define SNMP_SIZE_OBJECTID              128
 508 #define SNMP_SIZE_BUFCHR                256
 509 #define SNMP_SIZE_BUFINT                128
 510 #define SNMP_SIZE_SMALLOBJECTID         16
 511
 512 /* Requests */
 513 #define SNMP_PDU_GET                    0
 514 #define SNMP_PDU_NEXT                   1
 515 #define SNMP_PDU_RESPONSE               2
 516 #define SNMP_PDU_SET                    3
 517 #define SNMP_PDU_TRAP1                  4
 518 #define SNMP_PDU_BULK                   5
 519 #define SNMP_PDU_INFORM                 6
 520 #define SNMP_PDU_TRAP2                  7
 521
 522 /* Errors */
 523 #define SNMP_NOERROR                    0
 524 #define SNMP_TOOBIG                     1
 525 #define SNMP_NOSUCHNAME                 2
 526 #define SNMP_BADVALUE                   3
 527 #define SNMP_READONLY                   4
 528 #define SNMP_GENERROR                   5
 529 #define SNMP_NOACCESS                   6
 530 #define SNMP_WRONGTYPE                  7
 531 #define SNMP_WRONGLENGTH                8
 532 #define SNMP_WRONGENCODING              9
 533 #define SNMP_WRONGVALUE                 10
 534 #define SNMP_NOCREATION                 11
 535 #define SNMP_INCONSISTENTVALUE          12
 536 #define SNMP_RESOURCEUNAVAILABLE        13
 537 #define SNMP_COMMITFAILED               14
 538 #define SNMP_UNDOFAILED                 15
 539 #define SNMP_AUTHORIZATIONERROR         16
 540 #define SNMP_NOTWRITABLE                17
 541 #define SNMP_INCONSISTENTNAME           18
 542
 543 /* General SNMP V1 Traps */
 544 #define SNMP_TRAP_COLDSTART             0
 545 #define SNMP_TRAP_WARMSTART             1
 546 #define SNMP_TRAP_LINKDOWN              2
 547 #define SNMP_TRAP_LINKUP                3
 548 #define SNMP_TRAP_AUTFAILURE            4
 549 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 550 #define SNMP_TRAP_ENTSPECIFIC           6
 551
 552 /* SNMPv1 Types */
 553 #define SNMP_NULL                0
 554 #define SNMP_INTEGER             1    /* l  */
 555 #define SNMP_OCTETSTR            2    /* c  */
 556 #define SNMP_DISPLAYSTR          2    /* c  */
 557 #define SNMP_OBJECTID            3    /* ul */
 558 #define SNMP_IPADDR              4    /* uc */
 559 #define SNMP_COUNTER             5    /* ul */
 560 #define SNMP_GAUGE               6    /* ul */
 561 #define SNMP_TIMETICKS           7    /* ul */
 562 #define SNMP_OPAQUE              8    /* c  */
 563
 564 /* Additional SNMPv2 Types */
 565 #define SNMP_UINTEGER            5    /* ul */
 566 #define SNMP_BITSTR              9    /* uc */
 567 #define SNMP_NSAP               10    /* uc */
 568 #define SNMP_COUNTER64          11    /* ul */
 569 #define SNMP_NOSUCHOBJECT       12
 570 #define SNMP_NOSUCHINSTANCE     13
 571 #define SNMP_ENDOFMIBVIEW       14
 572
 573 union snmp_syntax
 574 {
 575         unsigned char uc[0];    /* 8 bit unsigned */
 576         char c[0];              /* 8 bit signed */
 577         unsigned long ul[0];    /* 32 bit unsigned */
 578         long l[0];              /* 32 bit signed */
 579 };
 580
 581 struct snmp_object
 582 {
 583         unsigned long *id;
 584         unsigned int id_len;
 585         unsigned short type;
 586         unsigned int syntax_len;
 587         union snmp_syntax syntax;
 588 };
 589
 590 struct snmp_request
 591 {
 592         unsigned long id;
 593         unsigned int error_status;
 594         unsigned int error_index;
 595 };
 596
 597 struct snmp_v1_trap
 598 {
 599         unsigned long *id;
 600         unsigned int id_len;
 601         unsigned long ip_address;       /* pointer  */
 602         unsigned int general;
 603         unsigned int specific;
 604         unsigned long time;
 605 };
 606
 607 /* SNMP types */
 608 #define SNMP_IPA    0
 609 #define SNMP_CNT    1
 610 #define SNMP_GGE    2
 611 #define SNMP_TIT    3
 612 #define SNMP_OPQ    4
 613 #define SNMP_C64    6
 614
 615 /* SNMP errors */
 616 #define SERR_NSO    0
 617 #define SERR_NSI    1
 618 #define SERR_EOM    2
 619
 620 static inline void mangle_address(unsigned char *begin,
 621                                   unsigned char *addr,
 622                                   const struct oct1_map *map,
 623                                   __sum16 *check);
 624 struct snmp_cnv
 625 {
 626         unsigned int class;
 627         unsigned int tag;
 628         int syntax;
 629 };
 630
 631 static const struct snmp_cnv snmp_conv[] = {
 632         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 633         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 634         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 635         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 636         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 637         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 638         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 639         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 640         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 641         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 642
 643         /* SNMPv2 data types and errors */
 644         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 645         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 646         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 647         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 648         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 649         {0,       0,       -1}
 650 };
 651
 652 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 653                                          unsigned int cls,
 654                                          unsigned short *syntax)
 655 {
 656         const struct snmp_cnv *cnv;
 657
 658         cnv = snmp_conv;
 659
 660         while (cnv->syntax != -1) {
 661                 if (cnv->tag == tag && cnv->class == cls) {
 662                         *syntax = cnv->syntax;
 663                         return 1;
 664                 }
 665                 cnv++;
 666         }
 667         return 0;
 668 }
 669
 670 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 671                                         struct snmp_object **obj)
 672 {
 673         unsigned int cls, con, tag, len, idlen;
 674         unsigned short type;
 675         unsigned char *eoc, *end, *p;
 676         unsigned long *lp, *id;
 677         unsigned long ul;
 678         long l;
 679
 680         *obj = NULL;
 681         id = NULL;
 682
 683         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 684                 return 0;
 685
 686         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 687                 return 0;
 688
 689         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 690                 return 0;
 691
 692         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 693                 return 0;
 694
 695         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 696                 return 0;
 697
 698         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 699                 kfree(id);
 700                 return 0;
 701         }
 702
 703         if (con != ASN1_PRI) {
 704                 kfree(id);
 705                 return 0;
 706         }
 707
 708         type = 0;
 709         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 710                 kfree(id);
 711                 return 0;
 712         }
 713
 714         l = 0;
 715         switch (type) {
 716         case SNMP_INTEGER:
 717                 len = sizeof(long);
 718                 if (!asn1_long_decode(ctx, end, &l)) {
 719                         kfree(id);
 720                         return 0;
 721                 }
 722                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 723                 if (*obj == NULL) {
 724                         kfree(id);
 725                         return 0;
 726                 }
 727                 (*obj)->syntax.l[0] = l;
 728                 break;
 729         case SNMP_OCTETSTR:
 730         case SNMP_OPAQUE:
 731                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 732                         kfree(id);
 733                         return 0;
 734                 }
 735                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 736                 if (*obj == NULL) {
 737                         kfree(p);
 738                         kfree(id);
 739                         return 0;
 740                 }
 741                 memcpy((*obj)->syntax.c, p, len);
 742                 kfree(p);
 743                 break;
 744         case SNMP_NULL:
 745         case SNMP_NOSUCHOBJECT:
 746         case SNMP_NOSUCHINSTANCE:
 747         case SNMP_ENDOFMIBVIEW:
 748                 len = 0;
 749                 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 750                 if (*obj == NULL) {
 751                         kfree(id);
 752                         return 0;
 753                 }
 754                 if (!asn1_null_decode(ctx, end)) {
 755                         kfree(id);
 756                         kfree(*obj);
 757                         *obj = NULL;
 758                         return 0;
 759                 }
 760                 break;
 761         case SNMP_OBJECTID:
 762                 if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
 763                         kfree(id);
 764                         return 0;
 765                 }
 766                 len *= sizeof(unsigned long);
 767                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 768                 if (*obj == NULL) {
 769                         kfree(lp);
 770                         kfree(id);
 771                         return 0;
 772                 }
 773                 memcpy((*obj)->syntax.ul, lp, len);
 774                 kfree(lp);
 775                 break;
 776         case SNMP_IPADDR:
 777                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 778                         kfree(id);
 779                         return 0;
 780                 }
 781                 if (len != 4) {
 782                         kfree(p);
 783                         kfree(id);
 784                         return 0;
 785                 }
 786                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 787                 if (*obj == NULL) {
 788                         kfree(p);
 789                         kfree(id);
 790                         return 0;
 791                 }
 792                 memcpy((*obj)->syntax.uc, p, len);
 793                 kfree(p);
 794                 break;
 795         case SNMP_COUNTER:
 796         case SNMP_GAUGE:
 797         case SNMP_TIMETICKS:
 798                 len = sizeof(unsigned long);
 799                 if (!asn1_ulong_decode(ctx, end, &ul)) {
 800                         kfree(id);
 801                         return 0;
 802                 }
 803                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 804                 if (*obj == NULL) {
 805                         kfree(id);
 806                         return 0;
 807                 }
 808                 (*obj)->syntax.ul[0] = ul;
 809                 break;
 810         default:
 811                 kfree(id);
 812                 return 0;
 813         }
 814
 815         (*obj)->syntax_len = len;
 816         (*obj)->type = type;
 817         (*obj)->id = id;
 818         (*obj)->id_len = idlen;
 819
 820         if (!asn1_eoc_decode(ctx, eoc)) {
 821                 kfree(id);
 822                 kfree(*obj);
 823                 *obj = NULL;
 824                 return 0;
 825         }
 826         return 1;
 827 }
 828
 829 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
 830                                          struct snmp_request *request)
 831 {
 832         unsigned int cls, con, tag;
 833         unsigned char *end;
 834
 835         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 836                 return 0;
 837
 838         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 839                 return 0;
 840
 841         if (!asn1_ulong_decode(ctx, end, &request->id))
 842                 return 0;
 843
 844         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 845                 return 0;
 846
 847         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 848                 return 0;
 849
 850         if (!asn1_uint_decode(ctx, end, &request->error_status))
 851                 return 0;
 852
 853         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 854                 return 0;
 855
 856         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 857                 return 0;
 858
 859         if (!asn1_uint_decode(ctx, end, &request->error_index))
 860                 return 0;
 861
 862         return 1;
 863 }
 864
 865 /*
 866  * Fast checksum update for possibly oddly-aligned UDP byte, from the
 867  * code example in the draft.
 868  */
 869 static void fast_csum(__sum16 *csum,
 870                       const unsigned char *optr,
 871                       const unsigned char *nptr,
 872                       int offset)
 873 {
 874         unsigned char s[4];
 875
 876         if (offset & 1) {
 877                 s[0] = ~0;
 878                 s[1] = ~*optr;
 879                 s[2] = 0;
 880                 s[3] = *nptr;
 881         } else {
 882                 s[0] = ~*optr;
 883                 s[1] = ~0;
 884                 s[2] = *nptr;
 885                 s[3] = 0;
 886         }
 887
 888         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 889 }
 890
 891 /*
 892  * Mangle IP address.
 893  *      - begin points to the start of the snmp messgae
 894  *      - addr points to the start of the address
 895  */
 896 static inline void mangle_address(unsigned char *begin,
 897                                   unsigned char *addr,
 898                                   const struct oct1_map *map,
 899                                   __sum16 *check)
 900 {
 901         if (map->from == NOCT1(addr)) {
 902                 u_int32_t old;
 903
 904                 if (debug)
 905                         memcpy(&old, addr, sizeof(old));
 906
 907                 *addr = map->to;
 908
 909                 /* Update UDP checksum if being used */
 910                 if (*check) {
 911                         fast_csum(check,
 912                                   &map->from, &map->to, addr - begin);
 913
 914                 }
 915
 916                 if (debug)
 917                         printk(KERN_DEBUG "bsalg: mapped %pI4 to %pI4\n",
 918                                &old, addr);
 919         }
 920 }
 921
 922 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 923                                       struct snmp_v1_trap *trap,
 924                                       const struct oct1_map *map,
 925                                       __sum16 *check)
 926 {
 927         unsigned int cls, con, tag, len;
 928         unsigned char *end;
 929
 930         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 931                 return 0;
 932
 933         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 934                 return 0;
 935
 936         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 937                 return 0;
 938
 939         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 940                 goto err_id_free;
 941
 942         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 943               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 944                 goto err_id_free;
 945
 946         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 947                 goto err_id_free;
 948
 949         /* IPv4 only */
 950         if (len != 4)
 951                 goto err_addr_free;
 952
 953         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 954
 955         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 956                 goto err_addr_free;
 957
 958         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 959                 goto err_addr_free;
 960
 961         if (!asn1_uint_decode(ctx, end, &trap->general))
 962                 goto err_addr_free;
 963
 964         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 965                 goto err_addr_free;
 966
 967         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 968                 goto err_addr_free;
 969
 970         if (!asn1_uint_decode(ctx, end, &trap->specific))
 971                 goto err_addr_free;
 972
 973         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 974                 goto err_addr_free;
 975
 976         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 977               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 978                 goto err_addr_free;
 979
 980         if (!asn1_ulong_decode(ctx, end, &trap->time))
 981                 goto err_addr_free;
 982
 983         return 1;
 984
 985 err_addr_free:
 986         kfree((unsigned long *)trap->ip_address);
 987
 988 err_id_free:
 989         kfree(trap->id);
 990
 991         return 0;
 992 }
 993
 994 /*****************************************************************************
 995  *
 996  * Misc. routines
 997  *
 998  *****************************************************************************/
 999
1000 static void hex_dump(const unsigned char *buf, size_t len)
1001 {
1002         size_t i;
1003
1004         for (i = 0; i < len; i++) {
1005                 if (i && !(i % 16))
1006                         printk("\n");
1007                 printk("%02x ", *(buf + i));
1008         }
1009         printk("\n");
1010 }
1011
1012 /*
1013  * Parse and mangle SNMP message according to mapping.
1014  * (And this is the fucking 'basic' method).
1015  */
1016 static int snmp_parse_mangle(unsigned char *msg,
1017                              u_int16_t len,
1018                              const struct oct1_map *map,
1019                              __sum16 *check)
1020 {
1021         unsigned char *eoc, *end;
1022         unsigned int cls, con, tag, vers, pdutype;
1023         struct asn1_ctx ctx;
1024         struct asn1_octstr comm;
1025         struct snmp_object *obj;
1026
1027         if (debug > 1)
1028                 hex_dump(msg, len);
1029
1030         asn1_open(&ctx, msg, len);
1031
1032         /*
1033          * Start of SNMP message.
1034          */
1035         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1036                 return 0;
1037         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1038                 return 0;
1039
1040         /*
1041          * Version 1 or 2 handled.
1042          */
1043         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1044                 return 0;
1045         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1046                 return 0;
1047         if (!asn1_uint_decode (&ctx, end, &vers))
1048                 return 0;
1049         if (debug > 1)
1050                 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1051         if (vers > 1)
1052                 return 1;
1053
1054         /*
1055          * Community.
1056          */
1057         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1058                 return 0;
1059         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1060                 return 0;
1061         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1062                 return 0;
1063         if (debug > 1) {
1064                 unsigned int i;
1065
1066                 printk(KERN_DEBUG "bsalg: community: ");
1067                 for (i = 0; i < comm.len; i++)
1068                         printk("%c", comm.data[i]);
1069                 printk("\n");
1070         }
1071         kfree(comm.data);
1072
1073         /*
1074          * PDU type
1075          */
1076         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1077                 return 0;
1078         if (cls != ASN1_CTX || con != ASN1_CON)
1079                 return 0;
1080         if (debug > 1) {
1081                 static const unsigned char *const pdus[] = {
1082                         [SNMP_PDU_GET] = "get",
1083                         [SNMP_PDU_NEXT] = "get-next",
1084                         [SNMP_PDU_RESPONSE] = "response",
1085                         [SNMP_PDU_SET] = "set",
1086                         [SNMP_PDU_TRAP1] = "trapv1",
1087                         [SNMP_PDU_BULK] = "bulk",
1088                         [SNMP_PDU_INFORM] = "inform",
1089                         [SNMP_PDU_TRAP2] = "trapv2"
1090                 };
1091
1092                 if (pdutype > SNMP_PDU_TRAP2)
1093                         printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1094                 else
1095                         printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1096         }
1097         if (pdutype != SNMP_PDU_RESPONSE &&
1098             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1099                 return 1;
1100
1101         /*
1102          * Request header or v1 trap
1103          */
1104         if (pdutype == SNMP_PDU_TRAP1) {
1105                 struct snmp_v1_trap trap;
1106                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1107
1108                 if (ret) {
1109                         kfree(trap.id);
1110                         kfree((unsigned long *)trap.ip_address);
1111                 } else
1112                         return ret;
1113
1114         } else {
1115                 struct snmp_request req;
1116
1117                 if (!snmp_request_decode(&ctx, &req))
1118                         return 0;
1119
1120                 if (debug > 1)
1121                         printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1122                         "error_index=%u\n", req.id, req.error_status,
1123                         req.error_index);
1124         }
1125
1126         /*
1127          * Loop through objects, look for IP addresses to mangle.
1128          */
1129         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1130                 return 0;
1131
1132         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1133                 return 0;
1134
1135         while (!asn1_eoc_decode(&ctx, eoc)) {
1136                 unsigned int i;
1137
1138                 if (!snmp_object_decode(&ctx, &obj)) {
1139                         if (obj) {
1140                                 kfree(obj->id);
1141                                 kfree(obj);
1142                         }
1143                         return 0;
1144                 }
1145
1146                 if (debug > 1) {
1147                         printk(KERN_DEBUG "bsalg: object: ");
1148                         for (i = 0; i < obj->id_len; i++) {
1149                                 if (i > 0)
1150                                         printk(".");
1151                                 printk("%lu", obj->id[i]);
1152                         }
1153                         printk(": type=%u\n", obj->type);
1154
1155                 }
1156
1157                 if (obj->type == SNMP_IPADDR)
1158                         mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1159
1160                 kfree(obj->id);
1161                 kfree(obj);
1162         }
1163
1164         if (!asn1_eoc_decode(&ctx, eoc))
1165                 return 0;
1166
1167         return 1;
1168 }
1169
1170 /*****************************************************************************
1171  *
1172  * NAT routines.
1173  *
1174  *****************************************************************************/
1175
1176 /*
1177  * SNMP translation routine.
1178  */
1179 static int snmp_translate(struct nf_conn *ct,
1180                           enum ip_conntrack_info ctinfo,
1181                           struct sk_buff *skb)
1182 {
1183         struct iphdr *iph = ip_hdr(skb);
1184         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1185         u_int16_t udplen = ntohs(udph->len);
1186         u_int16_t paylen = udplen - sizeof(struct udphdr);
1187         int dir = CTINFO2DIR(ctinfo);
1188         struct oct1_map map;
1189
1190         /*
1191          * Determine mappping for application layer addresses based
1192          * on NAT manipulations for the packet.
1193          */
1194         if (dir == IP_CT_DIR_ORIGINAL) {
1195                 /* SNAT traps */
1196                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1197                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1198         } else {
1199                 /* DNAT replies */
1200                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1201                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1202         }
1203
1204         if (map.from == map.to)
1205                 return NF_ACCEPT;
1206
1207         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1208                                paylen, &map, &udph->check)) {
1209                 if (net_ratelimit())
1210                         printk(KERN_WARNING "bsalg: parser failed\n");
1211                 return NF_DROP;
1212         }
1213         return NF_ACCEPT;
1214 }
1215
1216 /* We don't actually set up expectations, just adjust internal IP
1217  * addresses if this is being NATted */
1218 static int help(struct sk_buff *skb, unsigned int protoff,
1219                 struct nf_conn *ct,
1220                 enum ip_conntrack_info ctinfo)
1221 {
1222         int dir = CTINFO2DIR(ctinfo);
1223         unsigned int ret;
1224         const struct iphdr *iph = ip_hdr(skb);
1225         const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1226
1227         /* SNMP replies and originating SNMP traps get mangled */
1228         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1229                 return NF_ACCEPT;
1230         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1231                 return NF_ACCEPT;
1232
1233         /* No NAT? */
1234         if (!(ct->status & IPS_NAT_MASK))
1235                 return NF_ACCEPT;
1236
1237         /*
1238          * Make sure the packet length is ok.  So far, we were only guaranteed
1239          * to have a valid length IP header plus 8 bytes, which means we have
1240          * enough room for a UDP header.  Just verify the UDP length field so we
1241          * can mess around with the payload.
1242          */
1243         if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1244                  if (net_ratelimit())
1245                          printk(KERN_WARNING "SNMP: dropping malformed packet src=%pI4 dst=%pI4\n",
1246                                 &iph->saddr, &iph->daddr);
1247                  return NF_DROP;
1248         }
1249
1250         if (!skb_make_writable(skb, skb->len))
1251                 return NF_DROP;
1252
1253         spin_lock_bh(&snmp_lock);
1254         ret = snmp_translate(ct, ctinfo, skb);
1255         spin_unlock_bh(&snmp_lock);
1256         return ret;
1257 }
1258
1259 static const struct nf_conntrack_expect_policy snmp_exp_policy = {
1260         .max_expected   = 0,
1261         .timeout        = 180,
1262 };
1263
1264 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1265         .me                     = THIS_MODULE,
1266         .help                   = help,
1267         .expect_policy          = &snmp_exp_policy,
1268         .name                   = "snmp",
1269         .tuple.src.l3num        = AF_INET,
1270         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_PORT),
1271         .tuple.dst.protonum     = IPPROTO_UDP,
1272 };
1273
1274 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1275         .me                     = THIS_MODULE,
1276         .help                   = help,
1277         .expect_policy          = &snmp_exp_policy,
1278         .name                   = "snmp_trap",
1279         .tuple.src.l3num        = AF_INET,
1280         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_TRAP_PORT),
1281         .tuple.dst.protonum     = IPPROTO_UDP,
1282 };
1283
1284 /*****************************************************************************
1285  *
1286  * Module stuff.
1287  *
1288  *****************************************************************************/
1289
1290 static int __init nf_nat_snmp_basic_init(void)
1291 {
1292         int ret = 0;
1293
1294         BUG_ON(nf_nat_snmp_hook != NULL);
1295         RCU_INIT_POINTER(nf_nat_snmp_hook, help);
1296
1297         ret = nf_conntrack_helper_register(&snmp_trap_helper);
1298         if (ret < 0) {
1299                 nf_conntrack_helper_unregister(&snmp_helper);
1300                 return ret;
1301         }
1302         return ret;
1303 }
1304
1305 static void __exit nf_nat_snmp_basic_fini(void)
1306 {
1307         RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);
1308         nf_conntrack_helper_unregister(&snmp_trap_helper);
1309 }
1310
1311 module_init(nf_nat_snmp_basic_init);
1312 module_exit(nf_nat_snmp_basic_fini);
1313
1314 module_param(debug, int, 0600);